Ceramic layer constituted of partially and fully stabilized zirconium oxide

ABSTRACT

The use of a physical mixture of partially stabilized and fully stabilized zirconium oxide powder for producing a thermal barrier coating results in good thermal barrier properties and good mechanical properties is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/EP2018/056215, having a filing date of Mar. 13, 2018, which is based on German Application No. 10 2017 206 063.8, having a filing date of Apr. 10, 2017, the entire contents both of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a ceramic layer system, for which partially stabilized and fully stabilized powder as physical mixture is or has been sprayed.

BACKGROUND

For high-temperature applications such as gas turbines, metallic substrates are often protected by ceramic thermal barrier coatings.

Typical thermal barrier coatings (TBC) comprise zirconium oxide which is partially stabilized, for example 8% by weight yttrium-stabilized zirconium oxide. Fully stabilized zirconium oxide is likewise known, and this then usually has a partially stabilized zirconia layer as bonding layer on the substrate. However, double-layer systems always suffer from the problem of the difference in coefficients of thermal expansion.

SUMMARY

An aspect relates to a ceramic thermal barrier coating system which comprises a substrate, wherein the substrate is either a metallic substrate based on a nickel or cobalt superalloy, or the substrate is composed of CMC. In some embodiments, the ceramic thermal barrier coating system also comprises a bonding layer which is, in the case of a metallic substrate metallic, wherein the metallic substrate is an MCrAlY alloy, wherein M is at least one of nickel and cobalt. In the case of a substrate composed of CMC, the ceramic thermal barrier coating system comprises a ceramic bonding layer and an outer ceramic thermal barrier coating, the coating comprising grains of both partially stabilized zirconium oxide and of fully stabilized zirconium oxide.

BRIEF DESCRIPTION

Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

FIG. 1 shows a ceramic thermal barrier coating system;

FIG. 2 shows a similar embodiment of a layer system in which, as indicated by the arrow, a concentration gradient C is present in the ceramic layer;

FIG. 3 shows the possibility of the substrate and/or the bonding layer having a machined structured surface (engineered surfaces) in order to achieve better adhesion of the ceramic thermal barrier coating to the substrate or bonding layer; and

FIG. 4 shows an illustrative embodiment proceeding from FIG. 1, 2 or 3, in which depressions or longitudinal cracks, which have been introduced.

DETAILED DESCRIPTION

It is proposed that a physical mixture of partially stabilized and fully stabilized zirconium oxide be used. Preference is given to using 8% by weight yttrium partially stabilized zirconium oxide (PSZ) and 22%-48% yttrium fully stabilized zirconium oxide (FSZ). The ranges given for the stabilization can vary, and it is likewise possible to change the type of stabilizers, e.g. ytterbium, europium, etc., or else mixtures can be used.

FIG. 1 shows a ceramic layer system 1′ according to embodiments of the invention comprising a substrate 4, a metallic bonding layer 7, in particular based on MCrAlY, and an outer ceramic thermal barrier coating 10 which comprises a physical mixture of partially stabilized and fully stabilized zirconium oxide (ZrO₂). M is nickel (Ni) and/or cobalt (Co).

To produce the ceramic thermal barrier coating 10, either powders composed of FSZ and PSZ are mixed with one another beforehand and sprayed or powders composed of FSZ and PSZ are combined within a spray nozzle and sprayed on together.

Other procedures are possible.

The proportion of FSZ in the mixture or in the TBC is in the range from 10% by weight to 90% by weight.

FIG. 2 shows a similar embodiment of a layer system 1″ in which, as indicated by the arrow, a concentration gradient C is present in the ceramic layer 10′, so that the proportion of the fully stabilized phase FSZ increases, for example, in an outward direction to the outermost surface 19.

The concentration gradient C can extend over the entire layer thickness of the ceramic layer 10′ or extend only over part of the layer thickness.

FIG. 3 shows, proceeding from FIG. 1 or 2, the possibility of the substrate 4, 4′ and/or the bonding layer 7 having a machined structured surface 13 (engineered surfaces) in order to achieve better adhesion of the ceramic thermal barrier coating 10, 10′, 10″ to the substrate 4′ or bonding layer 7′.

The structured surface 13 of the substrate 4′ or of the bonding layer 7 provides an at least 50% greater roughness compared to unmachined substrates 4 or unmachined bonding layers.

FIG. 4 shows an illustrative embodiment proceeding from FIG. 1, 2 or 3, in which depressions or longitudinal cracks 16′, 16″, which have been introduced subsequently, e.g. by means of a laser (laser engravings), or have been produced by means of appropriate coating processes or subsequent heat treatment processes or during coating (dense vertical cracks, DVC), are present extending from the outermost surface 19 of the ceramic thermal barrier coating 10, 10′, 10″.

The features of the cracks 16′, 16″, . . . or depressions 16′, 16″, . . . (FIG. 4) and/or the machined adhesion surface 13 (FIG. 3) can be combined with one another (FIGS. 2, 3, 4).

The substrate 4, 4′ (FIGS. 1, 2, 3, 4) can also be composed of CMC, in which case the bonding layer 7 is also ceramic.

Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the intention.

For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module. 

1. A ceramic thermal barrier coating system which comprises at least: a substrate, wherein the substrate is either a metallic substrate, based on a nickel or cobalt superalloy, or a substrate composed of CMC; having a bonding layer, which is either in the case of a metallic substrate metallic, wherein said metallic substrate is an MCrAlY alloy, wherein M is at least one of nickel and cobalt, or in the case of a substrate composed of CMC a ceramic bonding layer; and also an outer ceramic thermal barrier coating, which coating comprises grains both of partially stabilized zirconium oxide and of fully stabilized zirconium oxide.
 2. The ceramic thermal barrier coating system as claimed in claim 1, wherein the stabilization of the zirconium oxide is effected by means of yttrium oxide, in particular 8% for partial stabilization and/or from 22% to 48% for full stabilization.
 3. The ceramic thermal barrier coating system as claimed in claim 1, wherein the concentration of the fully stabilized zirconium oxide increases in the direction of the outermost surface of the ceramic thermal barrier coating.
 4. The ceramic thermal barrier coating system as claimed in claim 1, wherein the mixing ratio of PSZ and FSZ is constant over the entire thickness of the ceramic layer.
 5. The ceramic thermal barrier coating system as claimed in claim 1, wherein depressions or elongated vertical cracks which have been introduced by means of a laser or produced during the coating process or by means of an after-treatment method are present extending from the outermost surface of the ceramic layer.
 6. The ceramic thermal barrier coating system as claimed in claim 1, wherein the surface of the substrate or of the bonding layer on the substrate to which the ceramic layer or the bonding layer has been applied has been machined.
 7. The ceramic thermal barrier coating system as claimed in claim 1, wherein the proportion of FSZ is at least 10% by weight and not more than 90% by weight. 